1. Field of the Invention
The present invention relates to hearing aids. The invention further relates to a hearing aid in two parts connected with electrical wires. The invention more specifically concerns a hearing aid having a base part to be arranged outside the ear canal of a hearing aid user, and an ear plug part to be arranged in the ear canal of a hearing aid user. The invention further relates to a method for communicating between two parts of a hearing aid.
A hearing aid is an electronic portable device adapted to compensate a hearing deficit of a user by a microphone, amplifier and a receiver. Many types of hearing aids are made as a two part device with one part, an ear plug or ear piece, for being arranged in the ear canal of the hearing aid user, and another part, a base part, for being arranged outside the ear canal. Often the base part is arranged behind the ear, known as a behind-the-ear housing. The base part will usually comprise signal processing means, one or two microphones, and a battery. In modern hearing aids the receiver is often arranged in the ear plug part and connected with the signal processing means in the base part through electric wires. This type is sometimes referred to as a Receiver-In-The-Ear (RITE) hearing aid.
It is often suggested to arrange different transducers in the ear plug part. One example is a microphone in the ear plug, at the side proximally to the tympanic membrane, for transforming sounds in the ear canal into electrical signals. Such a microphone may have many purposes during fitting and during daily use of the hearing aid. Also, a temperature sensor, an accelerometer and EEG measuring electrodes are considered as transducers which could be relevant to arrange in the ear plug part. The electrical signal from such a transducer needs to be transferred to the signal processing means of the base part of the hearing aid, normally by an extra pair of wires, for further processing, e.g. input to acoustic processing, logging or transmission to a remote device. It has now been realized that one problem in having such a transducer, e.g. a microphone, is that the wires used for transferring the signal from the transducer to the base part may pick up electromagnetic interference. The electrical signal generated in a microphone may be relatively weak, e.g. 1-5 μV, and therefore rather sensitive to noise.
It has also now been realized that this problem is larger when a receiver is arranged in the ear plug, since the wires supplying the receiver signal, which may be 2 V at peak level, will be arranged close to the wires transferring the signal from a transducer. Therefore, there may be a risk that the receiver signal will induce noise into the wires carrying the transducer signal.
2. The Prior Art
US-A1-2004/0116151 describes a databus which can also be applied for a hearing aid between a base part and a peripheral component. This databus is described as needing transfer of power, clock and synchronization signal.
One problem is that the number of wires should be as low as possible in order to keep the total diameter of the bundle of wires connecting the two parts as small as possible. Each wire is connected both to the ear plug part and to the base part, e.g. through a connector. This connection will take up some space, and will in general be a weak point in the construction, i.e. there is a risk of losing the electrical connection at this point. Furthermore the connectors typically applied are relatively expensive components. Therefore, keeping the necessary number of connections to a minimum is to be preferred.